Bathtub shelf



FIG. 1 is a perspective view taken from the top, front and left end of a bathtub shelf showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is right end elevational view thereof;

FIG. 5 is a left end elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof. 

The ornamental design for a bathtub shelf, as shown and described. 